A rope type elevator includes a driving apparatus comprising a motor, a speed reducer, a sheave and a deflector wheel, and has a mechanism of subjecting a load of a cage to one end of a main rope (hereinafter referred to as a “rope”) wound around the sheave and a load of a counterweight to the other end of the rope to move up and down the cage and the counterweight by means of friction between the rope and the sheave.
The rope is generally formed by twisting together strands which are formed by twisting together steel wires. This steel rope satisfies a friction characteristic, an abrasion-resistance characteristic, a fatigue-resistance characteristic and the like required to drive the elevator and is high reliability.
However, since the rope is a consumable article, there is life. The life factors of the rope are classified into four categories, that is, fatigue resulting from bending and extending of the rope effected when the rope passes around the sheave, abrasion resulting from mutual movement of the wires, abrasion of wires present in the outermost layer of the rope due to their contact with wall surfaces of groove in the sheave, and corrosion caused by contact of the rope with air. Thus, for the purpose of reducing influence due to repeated bending of the rope effected when the rope passes around the sheave, a ratio D/d of a diameter D of the sheave to a diameter d of the rope has been set at 40 or more.
On the other hand, the diameter D of the sheave directly relates to a driving torque of the motor required to move go and down the cage. To reduce the size and weight of an elevator system including a motor, the diameter of the sheave must be reduced.
Further, the steel rope is wound around the sheave made of cast iron and is frictionally driven. Therefore, vibration and noise occur due to metal contact when the rope is caught in the sheave, thereby affecting comfortableness.
As means for solving these problems, in JP-A-7-267534 specification described is a method of reducing the sheave diameter as well as vibration and noise by using a rope which is formed by twisting together synthetic fibers such as aramid fibers that are more flexible than steel wires and coating with a resin such as urethane.
Further, in order to determine the life of a synthetic fiber rope coated with a resin, in JP-A-8-261972 specification described is a method of embedding a conductive carbon fiber, which is weaker than a synthetic fiber, in a synthetic fiber rope coated with a resin and checking by the voltage whether or not the conductive carbon fiber is broken to determine the life of the rope.
On the other hand, the higher the contact pressure with the sheave becomes, the shorter the life of the rope becomes. That is, the contact pressure (Prope) of the rope is proportional to tension F of the rope and is inversely proportional to the diameter D of the sheave. Thus, if the sheave diameter is reduced, the pressure increases (Prope nearly equals to F/(D/d)).
As means for solving this, in PCT WO 99/43,885 specification described is a method of using a flat-belt, which is formed by arranging in a line a plurality of strands formed by twisting together steel wires or synthetic fibers such as aramid fibers to coat these strands with a resin, to reduce pressure associated with contact with the sheave to extend the life of the resin coated on a surface of the flat-belt.
To reduce diameter of sheave of mechanical systems using a rope, including a rope type elevator, to reduce the size of an electric motor or hoist driving the sheave and to reduce a setting area of the mechanical system, it is necessary to suppress decreases in the life and strength of the rope associated with decrease in bending radius of the rope.
It is an object of the present invention to provide a safe and reliable rope by suppressing decreases in the life and strength of the rope if the bending radius of the rope is reduced.
It is another object of the present invention to provide a safe and reliable elevator by suppressing decreases in the life and strength of a rope if the sheave diameter is reduced.